jest-util 30.4.1: convertDescriptorToString

Clean-room public code sample — generation instructions

Write a brand-new, minimal, self-contained code sample in this clean-room directory.
Do not copy, paraphrase, or reference any existing project source. Work only from this spec.

A csx.json manifest scaffold already exists. Do not recreate it from memory. Preserve its case.goal, packages and symbols; fill its empty case.contract with exact assertions and correct its environment, commands and verifierAdapter for the files you generate.

Goal: verify jest-util.convertDescriptorToString in pkg:npm/jest-util@30.4.1
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:npm/jest-util@30.4.1
Demonstrate these symbols/APIs:
  - jest-util.convertDescriptorToString

Rules:
  - One focused purpose; the smallest project that proves the goal.
  - Include a contract test (test/contract.*) that runs OFFLINE and exits 0 exactly when the goal behavior works.
  - Pin every dependency with a lockfile so resolution is reproducible.
  - No secrets, credentials, or tokens. No real URLs (only example.com or localhost). No absolute paths.
  - No personal names, emails, company names, or project identifiers of any kind.
  - No binaries and no generated output (node_modules, dist, target, venv, .git, .env).
  - Keep it under 200 files and 256KB packed.

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import { convertDescriptorToString } from 'jest-util';

export { convertDescriptorToString };

/**
 * Formats a descriptor (string, number, named function/class, or undefined)
 * into a test block title.
 *
 * @param {string | number | Function | undefined} descriptor - The descriptor to format.
 * @param {string} [prefix] - Optional prefix for the formatted title.
 * @returns {string} The formatted descriptor string.
 */
export function formatTestBlockName(descriptor, prefix = '') {
  const converted = convertDescriptorToString(descriptor);
  return prefix ? `${prefix}: ${converted}` : converted;
}

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{
  "name": "sample-jest-util-convert-descriptor-to-string",
  "version": "1.0.0",
  "description": "Clean-room verification sample for jest-util.convertDescriptorToString",
  "license": "MIT-0",
  "type": "module",
  "main": "index.mjs",
  "scripts": {
    "test": "node test/contract.mjs"
  },
  "dependencies": {
    "jest-util": "30.4.1"
  }
}

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  "symbols": [
    "jest-util.convertDescriptorToString"
  ]
}

import assert from 'node:assert/strict';
import { convertDescriptorToString } from 'jest-util';
import { formatTestBlockName } from '../index.mjs';

// 1. convertDescriptorToString returns string descriptor as is
{
  assert.equal(
    convertDescriptorToString('user authentication service'),
    'user authentication service',
    'String descriptor should be returned unchanged'
  );
  assert.equal(
    convertDescriptorToString(''),
    '',
    'Empty string descriptor should be returned unchanged'
  );
}

// 2. convertDescriptorToString converts number descriptor to string representation
{
  assert.equal(
    convertDescriptorToString(42),
    '42',
    'Positive integer descriptor should be stringified'
  );
  assert.equal(
    convertDescriptorToString(0),
    '0',
    'Zero number descriptor should be stringified'
  );
  assert.equal(
    convertDescriptorToString(-10.5),
    '-10.5',
    'Negative decimal descriptor should be stringified'
  );
  assert.equal(
    convertDescriptorToString(NaN),
    'NaN',
    'NaN descriptor should be stringified'
  );
}

// 3. convertDescriptorToString converts undefined descriptor to string 'undefined'
{
  assert.equal(
    convertDescriptorToString(undefined),
    'undefined',
    'Explicit undefined descriptor should return "undefined"'
  );
  assert.equal(
    convertDescriptorToString(),
    'undefined',
    'Implicit undefined (missing argument) should return "undefined"'
  );
}

// 4. convertDescriptorToString extracts function name from named function or ES6 class
{
  function testSuiteHandler() {}
  class AuthenticationController {}
  const arrowHandler = () => {};

  assert.equal(
    convertDescriptorToString(testSuiteHandler),
    'testSuiteHandler',
    'Named function descriptor should return function name'
  );
  assert.equal(
    convertDescriptorToString(AuthenticationController),
    'AuthenticationController',
    'Named ES6 class descriptor should return class name'
  );
  assert.equal(
    convertDescriptorToString(arrowHandler),
    'arrowHandler',
    'Named arrow function descriptor should return identifier name'
  );

  const customNamed = () => {};
  Object.defineProperty(customNamed, 'name', { value: 'customSuiteName' });
  assert.equal(
    convertDescriptorToString(customNamed),
    'customSuiteName',
    'Function with custom name property should return that name'
  );
}

// 5. convertDescriptorToString throws Error when descriptor is an anonymous function without a name
{
  const anonymousFn = (function () {
    return function () {};
  })();
  Object.defineProperty(anonymousFn, 'name', { value: '' });

  assert.throws(
    () => convertDescriptorToString(anonymousFn),
    {
      name: 'Error',
      message: 'Invalid first argument, function () {}. It must be a named class, named function, number, or string.',
    },
    'Anonymous function with empty name property should throw Error'
  );
}

// 6. convertDescriptorToString throws Error when descriptor is null, boolean, object, or bigint
{
  const invalidCases = [
    { value: null, expectedMsg: 'Invalid first argument, null. It must be a named class, named function, number, or string.' },
    { value: true, expectedMsg: 'Invalid first argument, true. It must be a named class, named function, number, or string.' },
    { value: false, expectedMsg: 'Invalid first argument, false. It must be a named class, named function, number, or string.' },
    { value: {}, expectedMsg: 'Invalid first argument, [object Object]. It must be a named class, named function, number, or string.' },
    { value: [1, 2], expectedMsg: 'Invalid first argument, 1,2. It must be a named class, named function, number, or string.' },
    { value: 123n, expectedMsg: 'Invalid first argument, 123. It must be a named class, named function, number, or string.' },
  ];

  for (const { value, expectedMsg } of invalidCases) {
    assert.throws(
      () => convertDescriptorToString(value),
      {
        name: 'Error',
        message: expectedMsg,
      },
      `Descriptor ${String(value)} should throw invalid first argument Error`
    );
  }
}

// 7. formatTestBlockName helper formats test block names using convertDescriptorToString
{
  assert.equal(
    formatTestBlockName('Data Parser'),
    'Data Parser',
    'Helper should format string descriptor without prefix'
  );
  assert.equal(
    formatTestBlockName(100, 'Test ID'),
    'Test ID: 100',
    'Helper should format number descriptor with prefix'
  );
  class UserService {}
  assert.equal(
    formatTestBlockName(UserService, 'Suite'),
    'Suite: UserService',
    'Helper should format class descriptor with prefix'
  );
}

console.log('All jest-util.convertDescriptorToString contract assertions passed successfully.');